1. Field of the Invention
The present invention is broadly concerned with novel, isolated strains of bacteria (as well as modifications thereof) having the ability to control the weeds downy brome, Japanese brome, and/or jointed goatgrass. More particularly, it is concerned with a bacterial strain selected from the group consisting of Pseudomonas putida (FH160), Enterobacter taylorae (FH650), and Xanthomonas maltophilia (FH131) and mixtures thereof, and a method of use thereof in an area of planted wheat for weed control.
2. Description of the Prior Art
The widespread adoption of conservation tillage systems in semi-arid environments and a shift from standard-height to semidwarf wheat (Triticum aestivum L.) cultivars have been accompanied by a dramatic increase and spread of winter annual grass weeds in winter wheat (Morrow and Stahlman, Weed Science 32 (Suppl. 1):2-6 (1984); Wicks, In: Weed Control in Limited-Tillage Systems, A. F. Wiese (ed.), pages 77-92, Monograph 2, Weed Science Society of America (1985)). Downy brome (Bromus tectorum L.) and the related species Japanese brome (B. japonicus Thunb.) and cheat (B. secalinus L.) infest more than 14 million acres of wheat in the western United States (Kennedy et al., Soil Science Society of America Journal 55:722-727 (1991)), and up to 1 million acres are infested annually with bromes in Kansas (Harris and Stahlman, Agronomy Abstracts, page 250, American Society of Agronomy (1991)). Jointed goatgrass (Aegilops cylindrica Host.) is another increasingly troublesome grass weed because it out-crosses with wheat. Jointed goatgrass infests an estimated 3-4 million acres of wheat in 10 Great Plains and western states, including about 400,000 acres in Kansas (Donald and Ogg, Weed Technology 5:3-17 (1991)) .
Studies indicate that downy brome can be highly competitive with winter wheat (Stahlman and Miller, Weed Science 38:224-228 (1990)). Densities of 24, 40, and 65 down brome plants m.sup.-2 reduced winter wheat yields by 10, 15, and 20%, respectively, when the downy brome emerged within 14 days after wheat emergence. Annual brome densities of 100 to 200 plants m.sup.-2 are common and occasionally exceed 400 m.sup.-2.
Metribuzin [4-amino-6-(1,1-dimethylethyl)-3-(methylthio)-1,2,4-triazin-5(4H)-one] is the only herbicide registered for postemergence control of Bromus spp. in a few tolerant winter wheat cultivars, but its high cost and restriction to tolerant cultivars have limited acceptance and use. More recently, diclofop [(.+-.)-2-(4-(2,4-dichlorophenoxy) phenoxy)propanoic acid], triallate [S-(2,3,3-trichloro-2-propenyl)bis(1-methylethyl)carbamothioate], and trifluralin [2,6-dinitro-N,N-dipropyl-4-(trifluoromethyl)benzenamine] were registered for preplant application to control certain Bromus spp. However, growers prefer postemergence herbicides because the density of annual bromes can vary widely and they want to assess the need before applying herbicides. Trifluralin is the only herbicide registered for suppression or partial control of jointed goatgrass.
Bacteria can suppress plant growth by the production of phytotoxic substances absorbed by the plant root (Suslow and Schroth, Phytopathology 72:111-115 (1982)). The inhibitory influence of these antagonistic bacteria has been shown to be both species and cultivar specific (Elliott and Lynch, Soil Biology and Biochemistry 16:69-71 (1984)). Because of this specificity, these bacteria have potential for controlling weeds growing in crops.
Microbial herbicides are indigenous living plant pathogens which control target weeds. These organisms have been applied to target weeds as sprays either alone or in combination with chemical herbicides. Two mycoherbicides, DEVICE and COLLEGO, have been developed from specific fungal pathogens of weeds and are successful commercial products (Templeton et al., Reviews of Weed Science 2:1-14 (1986)). However, bacteria have been commercially developed only in a few cases.
USDA researchers at Washington State University have isolated several bacteria which attack the roots of downybrome (Elliott and Kennedy, U.S. Pat. No. 5,030,562 (1991)). These bacteria are Pseudomonas spp. isolated from the rhizosphere/rhizoplane of several crop and weed species. A field study in 1988 indicated that one bacterial isolate (D7) reduced downy brome biomass by more than 50%, thus increasing the competitiveness of the wheat. The enhanced competitiveness resulted in a 35% yield increase compared to untreated wheat (Kennedy et al., Soil Science of America Journal 55:722-727 (1991)).
Although the use of plant-suppressive rhizobacteria has been reported for downy brome in the Pacific Northwest, the ability of these microorganisms to consistently control downy brome under the harsher conditions (higher temperatures and lower moisture) which exist in the Central Great Plains was not assessed. The ability of these bacteria to successfully inhibit weed growth depends upon many characteristics, including the cultural and climatic conditions present at the site, and the unique conditions during the inhibitory process. Therefore, the ability of a particular microorganism to reduce the growth of a weed cannot be predicted from the behavior of other microorganisms used for similar purposes.